Hydrochloric Acid → 2-(2-Formamidothiazol-4-yl)-2-(2-tert-butoxycarbonylaminoethoxyimino)acetic acid

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A mixture of 2-(2-formamidothiazol-4-yl)-2-(2-aminoethoxyimino)acetic acid (syn isomer, 0.80 g.) and triethylamine (0.45 g.), in a solution of a saturated aqueous solution of sodium bicarbonate (4 ml.), tetrahydrofuran (35 ml.) and water (25 ml.) was adjusted to pH 8.5 with hydrochloric acid. 2-Phenyl-2-(tert-butoxycarbonyloxyimino)acetonitrile (0.77 g.) was added to the stirred solution and stirred at room temperature for 3 hours. After distilling off tetrahydrofuran from the resultant solution, the aqueous solution was washed with diethyl ether, and adjusted to pH 1.5 with 85% phosphoric acid. The solution was extracted with ethyl acetate (50 ml.), and the extract was washed with a saturated aqueous solution of sodium chloride (10 ml.), dried over magnesium sulfate and concentrated under reduced pressure to give 2-(2-formamidothiazol-4-yl)-2-(2-tert-butoxycarbonylaminoethoxyimino)acetic acid (syn isomer, 0.40 g.).

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